Gear mechanism and blade drive device

ABSTRACT

A gear mechanism includes a pair of gears including first and second gears overlapped with each other in an axial direction. The first and second gears include first and second tooth portions, respectively. The first tooth portion slightly projects outwardly from the second tooth portion. The first gear is formed with a deformation facilitating portion for facilitating deformation of the first gear in a radial direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of and claims priority to International Patent Application No. PCT/JP2008/069096 filed on Oct. 22, 2008, which claims priority to Japanese Patent Application No. 2007-311296 filed on Nov. 30, 2007, subject matter of these patent documents is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to gear mechanisms and blade drive devices.

2. Description of the Related Art

There are wide varieties of mechanisms which transmit a drive force from a motor or an engine to another member and which employ plural gears. When the gear is employed as a drive transmitting mechanism, there may be a problem with an operation noise on the basis of backlash between gears meshing each other. Japanese Unexamined Utility Model Publication No. 53-122576 discloses a gear having at least one gear element and an elastic member jointed to the gear element, and an outer edge of the elastic member slightly projecting from that of the gear element. When such a gear is employed in the drive transmitting mechanism, the operation noise may be reduced, because the elastic member absorbs the impact caused by meshing the opposite gear therewith.

However, the operation noise according to the backlash of the gears may be needed to be further reduced depending on a product employing such gears. The same demand applies to, for example, a blade drive device employed in an optical device such as a camera.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a gear mechanism and a blade drive device each having an operation noise that is reduced.

According to an aspect of the present invention, there is provided a gear mechanism including: a pair of gears including first and second gears overlapped with each other in an axial direction, wherein: the first and second gears include first and second tooth portions, respectively; the first tooth portion slightly projects outwardly from the second tooth portion; and the first gear is formed with a deformation facilitating portion for facilitating deformation of the first gear in a radial direction.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will be described in detail with reference to the following drawings, wherein:

FIG. 1 is an exploded perspective view of the blade drive device according to the embodiment;

FIG. 2 is a front view of the blade drive device in which an electromagnetic actuator is assembled into a shutter plate;

FIG. 3 is a front view of the blade drive device in which a drive ring is further assembled into the shutter plate;

FIG. 4 is a front view of the blade drive device, in a fully opened state, in which an elastic gear, blades are further assembled into the shutter plate;

FIG. 5 is a front view of the blade drive device, in a small aperture state, in which the elastic gear, the blades are further assembled into the shutter plate;

FIG. 6 is a rear view of the blade drive device;

FIG. 7 is a view of a part of the blade drive device in the fully opened state;

FIGS. 8A to 8C are explanatory views of the meshing of teeth portions and a rotor pinion;

FIG. 9 is an explanatory view of the contact of the blade with the rotor pinion;

FIGS. 10A and 10B are enlarged views of the periphery of a drive pin positioned at an end portion of a cam slot;

FIGS. 11A and 11B are cross-sectional views of the periphery of the electromagnetic actuator;

FIG. 12 is an enlarged view of the periphery of an actuator chamber illustrated in FIG. 1;

FIGS. 13A and 13B are views partially illustrating the blade drive device according to a first variation;

FIG. 14 is an enlarged view of the periphery of a rotor pinion illustrated in FIG. 13A; and

FIGS. 15A and 15B are views partially illustrating a blade drive device according to a second variation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description will be given of an embodiment according to the present invention with reference to the drawings. FIG. 1 is an exploded perspective view of the blade drive device according to the embodiment. The blade drive device according to the embodiment includes: a blade support plate 10; blades 20 a to 20 c; an elastic gear 30 serving as a first gear; a drive ring 40 serving as a second gear; an electromagnetic actuator 50; a shutter plate 60; and a flexible printed circuit board 70, which are arranged in this order from the object side to the image side, when the object side is located to the upper side in FIG. 1 and the image side is located to the lower side in FIG. 1.

The blades 20 a to 20 c, the elastic gear 30, the drive ring 40, and the electromagnetic actuator 50 are housed between the blade support plate 10 and the shutter plate 60. The blade support plate 10 and the shutter plate 60 have openings 11 and 61, defining the optical path, at their center portions, respectively. The electromagnetic actuator 50 transmits its drive force to the blades 20 a to 20 c via the drive ring 40 and the elastic gear 30. The drive ring 40 has a ring shape. The drive ring 40 is partially provided with a teeth portion 43, serving as a second teeth portion to which the drive force is transmitted from the electromagnetic actuator 50, at its outer periphery. The drive ring 40 is slidably supported relative to the shutter plate 60. Specifically, a sliding edge 45 slidably contacts an inner edge portion 65.

Further, the drive ring 40 has plural drive pins 44 a to 44 c along the sliding edge 45 at even intervals. The drive pins 44 a to 44 c respectively engage engagement holes 34 a to 34 c formed in the elastic gear 30. The elastic gear 30 is fixed on the drive ring 40 to overlap it in the rotational axis direction, that is, in the optical axis direction. Furthermore, the elastic gear 30 is provided with a teeth portion 33, serving as a first teeth portion, at its outer periphery so as to overlap the teeth portion 43 in the optical axis direction. Also, a circular arc slot 32, which serves as a deformation facilitating portion and has a hole shape, is provided between the teeth portion 33 and the rotational center of the teeth portion 33.

Specifically, the circular arc slot 32, which serves as a deformation facilitating portion and has a hole shape, extends along the teeth portion 33. The elastic gear 30 also has an opening 31 defining the optical path at its center portion. The elastic gear 30 is thinner than the drive ring 40. Therefore, the elastic gear 30 is more deformable than the drive ring 40. Moreover, the elastic gear 30 is made deformable in the radial direction by the circular arc slot 32. In addition, the diameter of the opening 31 is smaller than those of the openings 11 and 61.

The blades 20 a to 20 c are arranged at the object side relative to the elastic gear 30. The blades 20 a to 20 c are provided with shaft holes 22 a to 22 c at their end portions, respectively. The shaft holes 22 a to 22 c respectively engage support shafts 62 a to 62 c formed on the shutter plate 60. This allows the blades 20 a to 20 c to be swingably supported with respect to the shutter plate 60. Moreover, the blades 20 a to 20 c are respectively provided with cam slots 24 a to 24 c. The cam slots 24 a to 24 c respectively engage the drive pins 44 a to 44 c. Therefore, by rotating the drive ring 40, the drive pins 44 a to 44 c are respectively moved within the cam slots 24 a to 24 c, and the blades 20 a to 20 c are respectively swung about the shaft holes 22 a to 22 c. Accordingly, the opening areas of the openings 11, 31, and 61 are adjustable. Consequently, the drive ring 40 serves as a drive member for transmitting the drive force from the electromagnetic actuator 50 to the blades 20 a to 20 c.

Further, the blade support plate 10 is provided with escape holes 14 a to 14 c, for reliving the drive pins 44 a to 44 c, in the vicinity of the opening 11. Furthermore, the blade support plate 10 is provided with a shaft hole 15 supporting a rotary shaft 54 of the electromagnetic actuator 50, as will be described later in more detail. Engagement pawls 191, which are formed at an edge portion of the blade support plate 10, engage engagement portions 691, which are formed at an outer edge portion 66 of the shutter plate 60. Engagement holes 192, which are formed in the blade support plate 10, fit projective portions 692, which are formed at the outer edge portion 66 of the shutter plate 60. In this manner, the blade support plate 10 is attached to the shutter plate 60.

The flexible printed circuit board (hereinafter referred to as FPC) 70, serving as a printed substrate, has a flexibility, and is fixed to the shutter plate 60 at an outer side surface thereof defining an actuator chamber AC housing the electromagnetic actuator 50. The FPC 70 is electrically connected to the electromagnetic actuator 50 and ensures the supply of electric power for the electromagnetic actuator 50.

FIG. 2 is a front view of the blade drive device in which the electromagnetic actuator 50 is assembled into the shutter plate 60. Referring to FIGS. 1 and 2, a blade chamber SC for housing the blades 20 a to 20 c and the actuator chamber AC for housing the electromagnetic actuator 50 are provided in the shutter plate 60. The actuator chamber AC projects to the image side in the optical axis direction relative to the blade chamber SC, and has a recess shape. The electromagnetic actuator 50 includes a rotor 51, a stator 52, coils 53 a and 53 b, and a rotor pinion 55, as illustrated in FIG. 2. The rotor 51 is magnetized to have different polarities in its circumferential direction. The rotary shaft 54 supports the rotor 51 and the rotor pinion 55 for integral rotation.

Moreover, as will be described later in more detail, the rotor pinion 55 is integrated with the rotary shaft 54 which is not indicated by the reference numeral in FIG. 2. Also, the rotary shaft 54, the rotor pinion 55 and the rotor 51 are formed by insert molding. Thus, the rotary shaft 54, the rotor pinion 55, and the rotor 51 are integrally formed. The stator 52 has a letter U shape and two arm portions, around which the coils 53 a and 53 b are respectively wound. The end portions of the coils 53 a and 53 b are electrically connected to the FPC 70. The stator 52 is excited by energization of the coils 53 a and 53 b, so that the magnetic force generated between the stator 52 and rotor 51 rotates the rotor 51 by a given range.

Further, the actuator chamber AC is provided with five boss portions 63 serving to align the electromagnetic actuator 50. Furthermore, four escape holes 671, which escape the end portions of the coils 53 a and 53 b outwardly from the actuator chamber AC, are provided in the vicinity of the actuator chamber AC. The two escape holes 671 are provided in the vicinity of the opening 61, and the remaining two escape holes 671 are provided at the outer periphery side. The end portions of the coils 53 a and 53 b are escaped outwardly through the escape holes 671, and are connected to solder land portions of the FPC 70 serving as a printed substrate, thereby attaining the electrical connection. These arrangements will be described later in more detail.

FIG. 3 is a front view of the blade drive device in which the drive ring 40 is further assembled into the shutter plate 60. As illustrated in FIG. 3, the drive ring 40 serving as a driven member is assembled to mesh the teeth portion 43 with the rotor pinion 55.

FIG. 4 is a front view of the blade drive device, in a fully opened state, in which the elastic gear 30, the blades 20 a to 20 c are further assembled into the shutter plate 60. FIG. 5 is a front view of the blade drive device, in a small aperture state, in which the elastic gear 30, the blades 20 a to 20 c are further assembled into the shutter plate 60. Referring to FIG. 4, the blade drive device is brought into the fully opened state by positioning the blades 20 a to 20 c in receded positions receded from the openings 31 and 61. Also, referring to FIG. 5, the small aperture state, in which the opening amounts of the openings 31 and 61 are reduced, is defined by positioning the blades 20 a to 20 c to cover the openings 31 and 61.

When the rotor pinion 55 rotates clockwise from the state illustrated in FIG. 4, the drive ring 40 rotates counterclockwise, whereas the blades 20 a to 20 c swing clockwise, thereby shifting the state to the state illustrated in FIG. 5.

FIG. 6 is a rear view of the blade drive device. The FPC 70 is fixed to the outer wall, defining the actuator chamber AC of the shutter plate 60, at the image side by use of a double-faced tape or the like.

FIG. 7 is a view of a part of the blade drive device in the fully opened state. FIG. 7 illustrates the elastic gear 30, the drive ring 40, the blade 20 a, the rotor 51, and the rotor pinion 55, in order to facilitate the understanding of the embodiment. The elastic gear 30 is arranged at the object side relative to the drive ring 40. In the fully opened state, the outer edge of the blade 20 a contacts the rotor pinion 55. This will be described later in more detail. Additionally, the elastic gear 30 and the drive ring 40 are fixed to each other such that the teeth portions 33 and 43 are slightly misaligned. Further, the elastic gear 30 is made thinner than the drive ring 40. Specifically, the thickness of the elastic gear 30 is reduced to about one-sixth of that of the drive ring 40. Further, the elastic gear 30 is made of a synthetic resin such as polyethylene terephthalate or acrylate resin, and is formed into a film shape. For this reason, the elastic gear 30 is made of a material which is more deformable that of than the drive ring 40 which is made of a general material such as polyacetal resin or nylon resin. As exemplified the material of the elastic gear 30 above, the material of the elastic gear 30 is not limited to the above one, and may be any one that is more deformable than the drive ring 40.

Next, a description will be given of meshing of the teeth portions 33 and 43 and the rotor pinion 55. FIGS. 8A to 8C are explanatory views of the meshing of the teeth portions 33 and 43 and the rotor pinion 55. FIG. 8A illustrates the state after the teeth portions 33 and 43 mesh the rotor pinion 55. FIG. 8B illustrates the state before the teeth portions 33 and 43 mesh the rotor pinion 55. FIG. 8C illustrates an enlarged part of FIG. 8B. Additionally, the rotor pinion 55 is also illustrated in FIGS. 8A to 8C, in order to facilitate the understanding of the embodiment.

Referring to FIG. 8A, the teeth portion 33 includes plural tooth portions 33 a, 33 b . . . , and the teeth portion 43 also includes plural tooth portions 43 a, 43 b . . . . As illustrated in FIG. 8A, a tooth tip 331 a of the tooth portion 33 a radially and outwardly projects from a tooth tip 431 a of the tooth portion 43 a. Further, one tooth surface 332 a of the tooth portion 33 a projects from one tooth surface 432 a of the tooth portion 43 a in the circumferential direction. Furthermore, the other tooth surface 333 a of the tooth portion 33 a substantially overlaps the other tooth surface 433 a of the tooth portion 43 a. This configuration also applies the tooth portions 33 b and 43 b adjacent to each other. In addition, the rotor pinion 55 includes plural tooth portions 55 a . . . . One tooth surface 552 a of the tooth portion 55 a contacts the tooth surface 332 b, and the other tooth surface 553 a of the tooth portion 55 a contacts both of the tooth surfaces 333 a and 433 a.

Further, the elastic gear 30 is provided with the circular arc slot 32 extending along the teeth portion 33 in the circumferential direction, as illustrated in FIG. 7. By providing the circular arc slot 32, the elastic gear 30 is elastically deformed, specifically, in the radial direction with ease. Thus, the circular arc slot 32 serves as a deformation facilitating portion for facilitating the elastic deformation of the elastic gear 30. Moreover, since the elastic gear 30 and the drive ring 40 are fixed to and overlapped with each other in the axial direction by fitting the drive pins 44 a to 44 c into the engagement holes 34 a to 34 c, respectively, the elastic gear 30 and the drive ring 40 serve as a pair of gears. Furthermore, the rotor pinion 55 serves as a mating gear meshing the pair of gears.

In this way, since the teeth portion 33 projects outwardly from the teeth portion 43, when the rotor pinion 55 meshes the teeth portions 33 and 43, the teeth portion 33 initially meshes the rotor pinion 55 in priority to the teeth portion 43. Moreover, since the teeth portion 33 is readily deformed in the radial direction at the circumferential range by providing the circular arc slot 32 in the elastic gear 30, the teeth portion 33 is allowed to mesh the rotor pinion 55, to be closer than to the teeth portion 43. This suppresses the backlash between the rotor pinion 55, and the elastic gear 30 and the drive ring 40 serving as a pair of gears. That is, the rotor pinion 55, and the elastic gear 30 and the drive ring 40 are always suppressed from rattling such that the axis of the rotor pinion 55 is spaced apart from those of the elastic gear 30 and the drive ring 40. This reduces the operation noise caused by the axial backlash generated between the rotary shaft 54 and the shaft hole 15 formed in the blade support plate 10, between the rotary shaft 54 and a shaft hole 64 formed in the shutter plate 60, or between the drive ring 40 and the inner edge portion 65 provided in the shutter plate 60.

Additionally, the projection amount of the tooth surface 332 a from the tooth surface 432 a in the circumferential direction is different from that of the tooth surface 333 a from the tooth surface 433 a. That is, the tooth surface 552 a contacts the tooth surface 332 b, whereas the tooth surface 553 a contacts both of the tooth surfaces 333 a and 433 a. Unlike the elastic gear 30, the drive ring 40 does not employ a configuration for facilitating its elastic deformation. Thus, the amount of the elastic deformation of the elastic gear 30 is variable in response to the rotational direction of the rotor pinion 55. That is, when the rotor pinion 55 rotates counterclockwise, the tooth surface 332 b serves as a transmitted surface to which the drive force is transmitted from the rotor pinion 55, whereas, when the rotor pinion 55 rotates clockwise, the tooth surfaces 333 a and 433 a serve as transmitted surfaces to which the drive force is transmitted from the rotor pinion 55. Accordingly, when the rotor pinion 55 rotates counterclockwise, since the tooth surface 332 b is elastically deformed with ease, the tooth surfaces 552 a and 332 b constantly contact each other to transmit the drive force from the rotor pinion 55. This mainly suppresses the backlash caused between the rotor pinion 55 and the drive ring 40 in the normal line direction, and also reduces the operation noise caused by the backlash. Further, when the rotor pinion 55 rotates clockwise, the transmission accuracy of the rotational drive force is mainly improved by contacting the tooth surface 433 a with the tooth surface 553 a.

Further, when the rotor pinion 55 rotates clockwise, the blades 20 a to 20 c swing in such a direction to reduce the opening areas of the openings 11, 31, and 61. Thus, the drive force is transmitted from the rotor pinion 55 to the tooth surfaces 433 a and 433 b, in the process for reducing the opening areas. For this reason, the drive force is transmitted to the teeth portion 43 of the drive ring 40 which does not employ the configuration for facilitating the elastic deformation. Consequently, the accuracy of the aperture can be maintained.

Next, a description will be given of the state of the teeth portions 33 and 43 before meshing the rotor pinion 55. Referring to FIGS. 8B and 8C, the tooth surface 333 a slightly projects outwardly from the tooth surface 433 a in the circumferential direction. In the state before the mesh, the projection amount of the tooth surface 332 a from the tooth surface 432 a in the circumferential direction is also different from that of the tooth surface 333 a from the tooth surface 433 a. This configuration also applies the tooth surfaces 333 b and 433 b. In the design of the distance between the axis of the rotor pinion 55, and the axes of the elastic gear 30 and the drive ring 40, it is necessary to consider the projection amount of the tooth surface 333 a from the tooth surface 433 a. That is, it is necessary to design the distance between the axis of the rotor pinion 55, and the axes of the elastic gear 30 and the drive ring 40, such that the projection amount of the tooth surface 333 a from the tooth surface 433 a is made zero by a pressing force of the rotor pinion 55 pressed against the elastic gear 30, so that the tooth surfaces 433 a and 333 a are substantially overlapped with each other. This suppresses the backlash and improves the transmission accuracy of the rotational drive force.

Next, a description will be given of the elastic gear 30 in more detail. As illustrated in FIGS. 1 and 7, the circular arc slot 32 is arranged along the teeth portion 33 partially provided at the outer edge of the elastic gear 30, is arranged between the teeth portion 33 and its rotation center, and extends in the circumferential direction. With such a configuration, the elastic deformation of the elastic gear 30 in a radial direction can be facilitated in its circumferential range.

Further, the elastic gear 30 and the drive ring 40 are fixed to each other by respectively engaging the drive pins 44 a to 44 c with the engagement holes 34 a to 34 c. Therefore, the drive pins 44 a to 44 c and the engagement holes 34 a to 34 c serve as engagement means for fixing them by engaging. In this manner, the elastic gear 30 and the drive ring 40 can be fixed to each other by a simple structure, thereby improving the assembling workability.

Furthermore, the engagement holes 34 a to 34 c are arranged at the radially inner side from the circular arc slot 32. This reason is as follows. When the means for fixing the elastic gear 30 and the drive ring 40 is provided at the radially inner side from the circular arc slot 32, the elastic gear 30 is fixed to the drive ring 40 at their portions located between the circular arc slot 32 and the rotor pinion 55. In this case, since it is difficult to transmit the pressing force of the rotor pinion 55 against the elastic gear 30 to the circular arc slot 32, the circular arc slot 32 dose not absorb the pressing force exerted from the rotor pinion 55, whereby the elastic deformation of the elastic gear 30 may be restricted in the radial direction.

Moreover, the drive pins 44 a to 44 c respectively engage the cam slots 24 a to 24 c. These engagements permit the drive force of the drive ring 40 to be transmitted to the blades 20 a to 20 c. In this manner, the drive ring 40 is provided with the structure for transmitting the drive force of the electromagnetic actuator 50 to the blades 20 a to 20 c. This is because when the elastic gear 30 is provided with the above structure, the drive force may not be transmitted with stability, since the elastic gear 30 is elastically deformable with ease.

Additionally, as mentioned above, the drive pins 44 a to 44 c have a function for transmitting the drive force of the electromagnetic actuator 50 to the blades 20 a to 20 c, and also have a function for fixing the elastic gear 30 to the drive ring 40. This reduces the number of the parts, since the fixing function and the transmitting function do not have to be separately provided. Moreover, the number of the parts is reduced, so that the space within the blade drive device can be effectively used, and the assembling workability is improved.

Further, as illustrated in FIGS. 1, 4, and 5, the rotor pinion 55, the teeth portions 43 and 33 serve as a gear mechanism for transmitting the drive force of the electromagnetic actuator 50 to the blades 20 a to 20 c. This gear mechanism is composed only of the rotor pinion 55 integrated with the rotor 51, and the elastic gear 30 and the drive ring 40 serving as a pair of gears. This reduces the number of the parts, as compared to a structure which transmits the drive force via many gears. This reduces the number of the meshing points of the gears, and also reduces the operation noise for them.

Next, a description will be given of the contact of the blade 20 a with the rotor pinion 55. FIG. 9 is an explanatory view of the contact of the blade 20 a with the rotor pinion 55. FIG. 9 is an enlarged view of the periphery of the rotor pinion 55 illustrated in FIG. 7. Additionally, any other members are omitted in FIG. 9. Referring to FIG. 4, the blade 20 a contacts the rotor pinion 55 with the opening area being in the fully opened state. This contact stops the rotation of the rotor pinion 55. Thus, the blade 20 a serves as stop means for being into and contact with the rotor pinion 55 and for stopping the rotation of the rotor pinion 55 by contacting the rotor pinion 55. Therefore, the rotations of the elastic gear 30 and the drive ring 40 are stopped, thereby causing the blades 20 a to 20 c to be located at the receded positions.

Further, the rotor pinion 55 is arranged closer to the electromagnetic actuator 50 than to the drive ring 40 in the transmitting pass on which the drive force is transmitted from the electromagnetic actuator 50 to the blades 20 a to 20 c. Thus, by directly stopping the rotor pinion 55, the transmission of this drive force can be disconnected before the drive force becomes greater in the process of transmitting the drive force of the electromagnetic actuator 50 to the blades 20 a to 20 c. Accordingly, this reduces the impact noise caused by the contact, as compared to a conventional case where the shutter plate 60 is provided with a projection shape stopper and the drive ring 40 is stopped by contacting this stopper.

Furthermore, although such stop means may be separately provided from the blade 20 a, the number of the parts can be reduced by employing the blade 20 a as the stop means.

Also, the blade 20 a contacts the rotor pinion 55 in the receded position. This reduces the influence to be applied on the opening area, even when the blade 20 a is vibrated by the impact, caused by the contact of the blade 20 a with the rotor pinion 55, or the like.

Moreover, as described above, since the rotor pinion 55, the rotary shaft 54, and the rotor 51 are integrated by insert molding, they integrally rotate. That is, the rotor pinion 55 and the rotor 51 integrally rotate. Thus, the rotor pinion 55 is a closest gear to the electromagnetic actuator 50 serving as a drive source. For example, like the conventional blade drive device, in a case where the drive force is transmitted via plural gears including an intermediate gear in order to reduce a rotational speed of the electromagnetic actuator 50, when the intermediate gear is contacted to be stopped, the following problem may occur. In such an intermediate gear, its rotational speed is reduced more than that of a gear closer to the drive source, and its torque is increased. This may increase the operation noise caused by the contact of the intermediate gear. However, as described in the present embodiment, the rotor pinion 55, which is closest to the drive source, is contacted by the blade 20 a and is then stopped, thereby stopping the rotation of the rotor pinion 55 with ease, and thereby also reducing the impact noise at that time.

Further, as illustrated in FIG. 9, the blade 20 a is provided with a cut-out portion 25 a at a position where the blade 20 a contacts the rotor pinion 55. The cut-out portion 25 a is formed such that the outer edge of the blade 20 a has a circular arc to be comparatively small. The curvature radius of the cut-out portion 25 a corresponds to the maximum radius from the center of the rotor pinion 55 to the tooth tip. As illustrated in FIG. 9, the length of the cut-out portion 25 a and the rotational position of the rotor pinion 55 are designed such that the cut-out portion 25 a contacts the two tooth portions 55 a and 55 b of the rotor pinion 55 when the blade 20 a is positioned at the receded position. Since the cut-out portion 25 a contacts the two tooth ends of the tooth portions 55 a and 55 b, the contact area of the blade 20 a and the rotor pinion 55 can be increased, thereby assisting in stopping the rotation of the rotor pinion 55. That is, the cut-out portion 25 a serves as an engagement structure for contacting the rotor pinion 55 to assist in stopping the rotation thereof.

Furthermore, the contact at two positions alleviates the impact. In addition, each of the blades 20 a to 20 c has a thin shape to facilitate its elastic deformation. This further alleviates the impact based on the contact of the blade 20 a with the rotor pinion 55. Also, referring to FIGS. 7 and 9, the cam slot 24 a is arranged close to the cut-out portion 25 a. This cam slot 24 a facilitates the elastic deformation of the blade 20 a in its drive direction. This cam slot 24 a is arranged in the vicinity of the contact position so as to absorb the impact caused by the contact. Further, since the cam slot 24 a extends along the arc edge of the blade 20 a having a fan shape, the cam slot 24 a can be enlarged relative to the blade 20 a, and the elastic deformation of the blade 20 a can be facilitated in its drive direction.

Next, a description will be given of the engagement of the cam slot 24 a and the drive pin 44 a. FIGS. 10A and 10B are enlarged views of the periphery of the drive pin 44 a positioned at an end portion of the cam slot 24 a. FIG. 10A illustrates the periphery of the drive pin 44 a in the fully opened state. FIG. 10B illustrates the periphery of the drive pin 44 a in the small aperture state where the opening area is minimum. The drive pin 44 a does not contact one end portion 241 a of the cam slot 24 a in the fully opened state, as illustrated in FIG. 10A. In contrast, the drive pin 44 a contacts the other end portion 242 a of the cam slot 24 a in the small aperture state, as illustrated in FIG. 10B. These arrangements apply the drive pins 44 b and 44 c and the cam slots 24 b and 24 c.

Therefore, in the small aperture state, the drive pins 44 a to 44 c contact end portions of the cam slots 24 a to 24 c, respectively, thereby stopping the drive ring 40 and positioning the blades 20 a to 20 c in such positions to cover the opening. As mentioned above, each of the blades 20 a to 20 c has a thin shape to facilitate its elastic deformation. Accordingly, this reduces the impact noise, as compared to a conventional case where the shutter plate 60 is provided with a stopper and the drive ring 40 contacts the stopper to stop. Additionally, the shutter plate 60 does not have to be provided with the stopper, thereby simplifying the structure. Moreover, the drive pins 44 a to 44 c simultaneously contact end portions of the cam slots 24 a to 24 c, respectively, thereby distributing the impact applied to each member.

Further, in the fully opened state, the blade 20 a contacts the rotor pinion 55 to stop the drive of the drive ring 40, as mentioned above. For example, when the blade 20 a contacts the rotor pinion 55 to be bent in the optical direction and runs onto a part of the rotor pinion 55, the drive pin 44 a contacts the one end portion 241 a to stop the drive of the drive ring 40.

In addition, although the drive pin 44 a does not contact the one end portion 241 a in the fully opened state, as illustrated in FIG. 10A, the drive pin 44 a may contact the one end portion 241 a. In this case, the drive pin 44 a and the blade 20 a simultaneously contacts the one end portion 241 a and the rotor pinion 55, respectively, thereby further distributing the impact applied to each member and reducing the operation noise.

Next, a description will be given of the electromagnetic actuator 50. FIGS. 11A and 11B are cross-sectional views of the periphery of the electromagnetic actuator 50. FIG. 11A is a cross sectional view taken along line A-A in FIG. 6. FIG. 11B is a partially enlarged view of FIG. 11A. Referring to FIG. 11A, the actuator chamber AC, which is defined at two boards between the shutter plate 60 and the blade support plate 10, is formed as a drive source chamber and houses the rotor 51, the stator 52, the rotary shaft 54 and the like. Further, the rotary shaft 54 has one end portion 541 which is located at the image side and which is supported for sliding with respect to the shaft hole 64. The rotary shaft 54 has the other end portion 542 which is located at the object side and which is supported for sliding by the shaft hole 15 formed in the blade support plate 10. Therefore, the rotary shaft 54 is rotatably supported between the blade support plate 10 and the shutter plate 60. Accordingly, the shutter plate 60 serves as a chassis for housing the electromagnetic actuator 50 and supporting the rotary shaft 54 for rotation.

As illustrated in FIG. 11B, the shaft hole 64 is filled with a lubricant L for lubricating the one end portion 541 and the shaft hole 64. Here, the diameter of the shaft hole 64 is made smaller toward the outside from the inside of the shutter plate 60. That is, the shaft hole 64 has a diameter slightly larger than that of the one end portion 541, and is conically shaped such that the diameter is smaller as apart from the one end portion 541. The shaft hole 64 passes through the actuator chamber AC. The FPC 70 is fixed at the outside of the shaft hole 64. The lubricant L is filled in a space defined by the one end portion 541, the shaft hole 64, and the FPC 70. An example of the lubricant L is a grease. In this manner, by filling the lubricant L, the operation noise in accordance with the rotation of the rotary shaft 54 can be reduced by means of a simple structure. Further, such a simple structure also suppresses the manufacturing cost.

Next, a description will be given of the assembling order in which the rotary shaft 54 is assembled into the shaft hole 64. First, the FPC 70 is fixed to the outer wall surface of the shutter plate 60, that is, to an image-side surface opposite to the actuator chamber AC by a double-faced tape. At this time, the shutter plate 60 is fixed to seal the shaft hole 64. Next, the lubricant L is filled in the shaft hole 64 from the actuator chamber AC side to the single shutter plate 60. The shaft hole 64 has a diameter becoming smaller to the outside from the inside of the actuator chamber AC, and is sealed with the FPC 70, as mentioned above. For this reason, when the lubricant with certain high viscosity is filled, the lubricant L may not be leaked out from the shaft hole 64.

Next, the stator 52, around which the coils 53 a and 53 b are wound, is press fitted into the actuator chamber AC with engaging the boss portions 63. Next, the one end portion 541, which is not provided with the rotor pinion 55, of a part in which the rotor pinion 55, the rotary shaft 54, and the rotor 51 are integrated, is inserted into the shaft hole 64. In this situation, the lubricant L within the shaft hole 64 is pressed outwardly from the actuator chamber AC, whereas the shaft hole 64 is shaped such that its diameter becomes smaller than that of the one end portion 541, as illustrated in FIG. 11B. Moreover, the shaft hole 64 is sealed with the FPC 70. For this reason, the one end portion 541 is merely inserted into a partway of the shaft hole 64, thereby suppressing the lubricant L from being leaked out from the shaft hole 64 by the pressure of the one end portion 541. Further, since the shaft hole 64 passes through the shutter plate 60, even after the one end portion 541 is inserted into the shaft hole 64, air mixed into the lubricant L can be leaked outwardly.

As mentioned above, the FPC 70 is fixed on the shutter plate 60 to seal the shaft hole 64 from its outside. This prevents the lubricant L from being leaked from the shaft hole 64 while the blade drive device operating. Further, the FPC 70 eliminates the necessity of separately providing a member for preventing the leak of the lubricant L, thereby reducing the number of the parts. In this manner, the rotary shaft 54 is assembled into the shaft hole 64.

In addition, since the shaft hole 64 is shaped such that its diameter is made smaller than that of the one end portion 541, the filled space, in which the lubricant L is filled, is prevented from being pressed by the rattling of the rotary shaft 54 in the axial direction, after the assembling of the blade drive device is accomplished. Further, the one end portion 541 of the rotary shaft 54 is located apart from the blades 20 a to 20 c, and the other end portion 542 is close to the blades 20 a to 20 c. Since the shaft hole 64 supports the one end portion 541 apart from the blades 20 a to 20 c, the lubricant L is suppressed from being leaked from the shaft hole 64 into the actuator chamber AC and being attached to the blades 20 a to 20 c, after the assembling is accomplished. Furthermore, the structure of the blade drive device is simpler in the far side from the blades 20 a to 20 c than near side thereto, thereby facilitating the work of filling the lubricant L, even in the assembling stage.

Next, a description will be given of a structure of the actuator chamber AC. FIG. 12 is an enlarged view of the periphery of the actuator chamber AC illustrated in FIG. 1. Referring to FIG. 12, the actuator chamber AC and the blade chamber SC are continuous with each other. That is, the actuator chamber AC and the blade chamber SC are provided between the blade support plate 10 and the shutter plate 60. In the conventional blade drive device, when the actuator serving as a drive source is formed into a single unit, its thickness in the optical axis direction is increased by the thickness of the shutter plate 60 and that of a cover of the unitized actuator. However, the configuration according to the present embodiment is capable of reducing the thickness in the optical axis direction. Further, as illustrated in FIGS. 11A and 11B, the rotor 51, the rotary shaft 54, and the rotor pinion 55 are integrated into a single unit, and their size is made minimum in the direction of the rotary shaft without the gap between the parts. Therefore, the parts are effectively arranged in the direction of the rotary shaft, thereby suppressing the increase in the thickness in the optical axis direction, and thereby reducing the number of the parts, and suppressing the manufacturing cost. In addition, the actuator chamber AC is provided with reliving holes 68 for relieving the thickness of the coils 53 a and 53 b in the optical axis direction.

Next, a description will be given of the structure for facilitating the wiring work of the coils 53 a and 53 b of the electromagnetic actuator 50. The FPC 70 is arranged on the outer surface opposite to the actuator chamber AC. Therefore, the lengths of the coils 53 a and 53 b extending to the FPC 70 can be shortened, so the coils 53 a and 53 b can be connected to the FPC 70 with ease. This facilitates the wiring work of the coils 53 a and 53 b. This also reduces the manufacturing cost.

Further, four escape holes 671 are provided in the vicinity of the actuator chamber AC of the shutter plate 60, as illustrated in FIG. 12. Each of the escape holes 671 has a slit shape. A guide groove 672 extends in the optical axis direction to be continuous with the escape hole 671. Here, the escape hole 671 and the guide groove 672 serve as openings for escaping the wires of the coils 53 a and 53 b outwardly from the actuator chamber AC serving as a drive source chamber. The guide groove 672 extends to the surface, of the shutter plate 60, on which the FPC 70 is fixed. The four guide grooves 672 correspond to the four escape holes 671. The work for wiring the coil is performed as follow. For example, after the FPC 70 is fixed to the outer wall surface, that is, to the image-side surface opposite to the actuator chamber AC, the electromagnetic actuator 50 is assembled into the actuator chamber AC. Next, one end of the coil 53 a extends outwardly from the escape hole 671 located near the one end, respectively. Then, the wire of the coil 53 a extends outwardly to the FPC 70 along the guide groove 672, and is connected to the solder land portion thereof. The above mentioned work also applies to the other end of the coils 53 a and 53 b. In this way, the escape holes 671 serves as escaping the wires of the coils 53 a and 53 b outwardly from the actuator chamber AC, and the guide grooves 672 serves as guiding the wires of the coils 53 a and 53 b to the FPC 70. These arrangements facilitate the work for wiring the coils 53 a and 53 b.

Next, a description will be given of a variation of the blade drive device. FIGS. 13A to 13B are views partially illustrating the blade drive device according to a first variation. Additionally, like the blade drive device mentioned above, the blade drive device according to the variation has three blades. The same components have the same reference numerals in order to avoid a duplicated description. FIG. 13A is a view partially illustrating the blade drive device according to the first variation. FIG. 13A illustrates, a drive ring 40A, a blade 20 aA, a rotor pinion 55A, and a gear train 80A. FIG. 13A illustrates a state in which the blade 20 aA is positioned at a receded position from an opening.

The rotor pinion 55A is press fitted onto a rotary shaft, not illustrated. By rotating the rotor pinion 55A, its drive force is transmitted to the gear train 80A, thereby meshing the gear train 80A with a teeth portion 43A partially formed in the outer periphery of the drive ring 40A. Therefore, the teeth portion 43A rotates to swing the blade 20 aA about a shaft hole 22 aA. FIG. 13B is an enlarged perspective view of the rotor pinion 55A. Referring to FIG. 13B, the rotor pinion 55A includes: a lower teeth portion 551A composed of plural tooth portions; and an upper teeth portion 552A composed of two tooth portions and overlapping the lower teeth portion 551A to shape two stages. The rotor pinion 55A is made of a synthetic resin. The lower teeth portion 551A and the upper teeth portion 552A are integrated. The drive force is transmitted to the gear train 80A via the lower teeth portion 551A.

FIG. 14 is an enlarged view of the periphery of the rotor pinion 55A illustrated in FIG. 13A. Referring to FIG. 14, a cut-out portion 25 aA is provided in the outer periphery of the blade 20 aA. When the blade 20 aA is positioned at the receded position, the cut-out portion 25 aA contacts the upper teeth portion 552A. Further, the lower teeth portion 551A is positioned at the rear side of the blade 20 aA. The upper teeth portion 552A is formed to serve as a projection portion projecting outwardly and radially. Thus, when the upper teeth portion 552A contacts the cut-out portion 25 aA, the upper teeth portion 552A engages the cut-out portion 25 aA, thereby stopping the rotation of the rotor pinion 55A. That is, the upper teeth portion 552A serves as an engagement structure to aid in stopping the rotation of the rotor pinion 55A with the blade 20 aA contacted with the rotor pinion 55A. With such a configuration, the rotation of the rotor pinion 55A is also stopped by a simple structure.

FIGS. 15A and 15B are views partially illustrating a blade drive device according to a second variation. FIG. 15A is a front view of the blade drive device in a fully opened state according to the second variation. FIG. 15B is a front view of the blade drive device in a fully closed view according to the second variation. Referring to FIGS. 15A and 15B, the blade drive device according to the second variation includes a blade 20 d in addition to the blades 20 a to 20 c. The blade 20 d is swingably supported by the support shaft 62 a, like the blade 20 a. The blade 20 d is arranged at the object side with respect to the blade 20 a. Further, the blade 20 d is provided with a cam slot 24 d having a circular arc shape. The cam slot 24 d engages the drive pin 44 a. In the state illustrated in FIG. 15A, that is, in the state where the opening is fully opened, the blade 20 d contacts the rotor pinion 55 to stop the rotation thereof. Thus, the blade 20 d serves as stop means for contacting the rotor pinion 55 and for stopping the rotation of the rotor pinion 55.

While the preferred embodiments of the present invention have been illustrated in detail, the present invention is not limited to the above-mentioned embodiments, and other embodiments, variations and modifications may be made without departing from the scope of the present invention.

In the above embodiments, the blade support plate 10 is arranged at the object side. However, the blade drive device may be configured such that the shutter plate 60 is arranged at the object side and the blade support plate 10 is arranged at the image side.

An intermediate gear may be provided between the rotor pinion 55 and the teeth portions 33 and 43 to contact the blade 20 a and stop the drive of the drive ring 40.

Although the elastic gear 30 and the drive ring 40 serve as a pair of gears, the present invention is not limited to these arrangements. For example, an intermediate gear may be employed as such a pair of gears.

In a case where an intermediate gear is employed as a pair of gears mentioned above, the other tooth surface, of the second tooth portion of the second gear not provided with a deformation facilitating portion, may transmit the drive force to a mating gear meshing the intermediate gear.

In the above embodiment, the elastic gear 30 is formed of a synthetic resin. However, a sheet member made of polyethylene terephthalate or acrylate resin, a generally antireflective film, a light shielding film such as a somablack film (SOMAR corporation) may be formed by pressing.

In the above embodiment, each of the blades 20 a to 20 c is made thin to be elastically deformable with ease. However, a manufacturing method of the blades is not limited to, and the blades may be formed by either molding or pressing.

In the above embodiment, the rotor pinion 55, the rotary shaft 54, the rotor 51 are integrated by inserting. However, all the rotor pinion 55 and the rotary shaft 54 may be integrated.

In the embodiment, a printed substrate employs the flexible printed circuit board 70. However, the printed substrate may employ a rigid substrate made of a material with rigidity, such as an epoxy resin

In the embodiment, although the escape holes 671 and the guide grooves 672 are formed in the shutter plate 60, these configurations may be formed in the blade support plate 10.

Finally, several aspects of the present invention are summarized as follows.

According to an aspect of the present invention, there is provided a gear mechanism including: a pair of gears including first and second gears overlapped with each other in an axial direction, wherein: the first and second gears include first and second tooth portions, respectively; the first tooth portion slightly projects outwardly from the second tooth portion; and the first gear is formed with a deformation facilitating portion for facilitating deformation of the first gear in a radial direction.

With such a configuration, the first tooth portion of the first gear projects outwardly from the second tooth portion of the second gear. Therefore, when the pair of gears meshes another gear, the first tooth portion mashes a tooth portion of another gear in priority to the second tooth portion. Further, the deformation facilitating portion, for facilitating the elastic deformation in the radial direction, is provided in the first gear. Another gear meshes the second gear not deformable while elastically deforming the first tooth portion. Therefore, the first tooth portion can be close meshed with a tooth portion of the other gear. This suppresses the backlash between the pair of gears and the other gear. That is, the rattling between the pair of gears and the other gear can be constantly prevented such that the center distance between the pair of gears and the other gear is larger. This specifically reduces the operation noise caused by the axial backlash in the direction between the axes of the pair of gears and the other gear.

In the above configuration, the deformation facilitating portion may be located between the first tooth portion and a rotation center of the first gear, and may extend in a circumferential direction of the first gear.

Such a configuration facilitates the radial elastic deformation of the first gear in a given circumferential range.

In the above configuration, the deformation facilitating portion may be formed in the first gear, and may have a hole shape.

Such a configuration enables the first gear to be deformed with ease in its radial direction by a simple structure.

In the above configuration, the first gear may be formed to be thin, and may be made of a material more elastically deformable than that of the second gear.

By such a configuration, the elastic deformation of the first gear can be facilitated.

In the above configuration, the first gear may have engagement means for fixing the first gear and the second gear by engagement, and the engagement means may be arranged at a radially inner side from the deformation facilitating portion.

The both are fixed by engagement, thereby improving the assembling workability. Further, the engagement means, which enables the both to be fixed, is arranged at a radially inner side with respect to the deformation facilitating portion, thereby eliminating a possibility of suppressing the elastic deformation of the first gear in its radial direction.

In the above configuration, a projection amount of the first tooth portion from the second tooth portion in one of circumferential directions may be different from that of the first tooth portion from the second tooth portion in the other of circumferential directions.

With such a configuration, the amount of the elastic deformation caused by the first gear is variable in response to the rotational direction of the pair of gears which meshes the other gear. Thus, when the pair of gears rotates in a given direction, the backlash can be suppressed in the direction of the normal line of the pair of gears and the other gear. Specifically, the operation noise, which is caused by the backlash in the direction of the normal line of the pair of gears and the other gear, can be reduced. When the pair of gears rotates in the reverse direction, the transmission accuracy of the rotational drive force can be improved.

In the above configuration, the gear mechanism may further include a mating gear meshing the pair of gears, one of tooth surfaces of the first tooth portion may project outwardly from one of tooth surfaces of the second tooth portion, the other of the tooth surfaces of the first tooth portion may substantially overlap the other of the tooth surfaces of the second tooth portion, one of tooth surfaces of a tooth portion of the mating gear may contact only the first tooth portion; and the other of the tooth surfaces of the tooth portion of the mating gear may contact the second tooth portion.

The one of tooth surfaces of the first tooth portion projects outwardly from the one of tooth surfaces of the second tooth portion, thereby suppressing the backlash. Also, the other of tooth surfaces of the first tooth portion substantially overlaps the other of the tooth surfaces of the second tooth portion, thereby keeping the transmission accuracy of the rotational drive force. Namely, this suppresses the backlash between the pair of gears and the mating gear, and also maintains the transmission accuracy of the rotational drive force.

According to another aspect of the present invention, there is provided a blade drive device including: a board having an opening; a blade changing an opening area of the opening; and a gear mechanism transmitting a drive force from a drive source to the blade, wherein: the gear mechanism includes a pair of gears including first and second gears overlapped with each other in an axial direction; the first and second gears include first and second tooth portions, respectively; the first tooth portion slightly projects outwardly from the second tooth portion; and the first gear is formed with a deformation facilitating portion for facilitating deformation of the first gear in a radial direction.

This reduces the operation noise of the blade drive device.

In the above configuration, the deformation facilitating portion may be located between the first tooth portion and a rotation center of the first gear, and may extend in a circumferential direction of the first gear.

This arrangement facilitates the radial elastic deformation of the first gear in a given circumferential range.

In the above configuration, the deformation facilitating portion may be formed in the first gear, and has a hole shape.

Due to such a configuration, the first gear is substantially shorter in its radial direction, thereby facilitating the deformation of the first gear in its radial direction.

In the above configuration, the first gear may have engagement means for fixing the first gear and the second gear by engagement, and the engagement means may be arranged at a radially inner side from the deformation facilitating portion, and engages the blade to transmit a rotational drive force of the pair of gears to the blade.

Since the both are fixed by engagement, the number of the parts can be reduced and the assemble workability can be improved. Further, since the engagement means, which fixes the both, is arranged at the radial inner side from the deformation facilitating portion, the radial elastic deformation of the first gear may not be restricted.

In the above configuration, the engagement means may include: a drive pin formed in the second gear; an engagement hole engaging the drive pin and formed in the first gear; and a cam slot engaging the drive pin and formed in the blade.

If the first gear is provided with a transmission structure for transmitting the rotational drive force to the blade, the rotational drive force may be transmitted unsteadily, since the first gear is provided with the deformation facilitating portion. However, by providing the transmission structure in the second gear, the rotational drive force is steadily transmitted to the blade. Further, the second gear serves to transmit the drive force from the drive source to the blade, and serves to fix the first gear to the second gear. With such a configuration, it is unnecessary to provide a fixing function separately from the transmission function, thereby reducing the number of the parts and effectively using the space. In addition, the assembling workability can be improved.

In the above configuration, a projection amount of the first tooth portion from the second tooth portion in one of circumferential directions may be different from that of the first tooth portion from the second tooth portion in the other of circumferential directions.

With such a configuration, the amount of the elastic deformation of the first gear is variable in response to the rotational direction, when the pair of gears meshes the other gear. Therefore, the backlash can be suppressed and the operation noise can be reduced when the pair of gears rotates in a given direction, and the transmission accuracy of the rotational drive force can be improved when the pair of gears rotates in the reverse direction.

In the above configuration, the gear mechanism may include a mating gear meshing the pair of gears, one of tooth surfaces of the first tooth portion may project outwardly from one of tooth surfaces of the second tooth portion, the other of tooth surfaces of the first tooth portion may substantially overlap the other of tooth surfaces of the second tooth portion, one of tooth surfaces of a tooth portion of the mating gear may contact only the first tooth portion, and the other of the tooth surfaces of the tooth portion of the mating gear may contact the second tooth portion.

This configuration suppresses the backlash and also maintains the transmission accuracy of the rotational drive force.

In the above configuration, the other of the tooth surfaces of the second tooth portion may be a tooth surface to which a drive force is transmitted by the mating gear or which transmits the drive force to the mating gear at a time when the area of the opening is reduced by the blade.

With such a configuration, the other of tooth surfaces of the second tooth portion, which is not provided with the facilitating elastic deformation portion, is the tooth surface, to which the drive force is transmitted from the mating gear, or which transmits the drive force to the mating gear, when the area of the opening is reduced. Therefore, the accuracy of reducing the opening can be maintained.

In the above configuration, the gear mechanism may include: the pair of gears; and a mating gear meshing the pair of gears and connected to a rotary shaft of the drive source.

With such a configuration, the gear mechanism only includes the pair of gears and the mating gear connected to the rotary shaft. This reduces the number of the parts and the operation noise.

In the above configuration, the first gear may be formed to be thin, and may be made of a material more elastically deformable than that of the second gear.

This arrangement facilitates the elastic deformation of the first gear. 

1. A gear mechanism comprising: a pair of gears including first and second gears overlapped with each other in an axial direction, wherein: the first and second gears include first and second tooth portions, respectively; the first tooth portion slightly projects outwardly from the second tooth portion; and the first gear is formed with a deformation facilitating portion for facilitating deformation of the first gear in a radial direction.
 2. The gear mechanism of claim 1, wherein the deformation facilitating portion is located between the first tooth portion and a rotation center of the first gear, and extends in a circumferential direction of the first gear.
 3. The gear mechanism of claim 1, wherein the deformation facilitating portion is formed in the first gear, and has a hole shape.
 4. The gear mechanism of claim 1, wherein the first gear is formed to be thin, and is made of a material more elastically deformable than that of the second gear.
 5. The gear mechanism of claim 1, wherein: the first gear has engagement means for fixing the first gear and the second gear by engagement; and the engagement means is arranged at a radially inner side from the deformation facilitating portion.
 6. The gear mechanism of claim 1, wherein a projection amount of the first tooth portion from the second tooth portion in one of circumferential directions is different from that of the first tooth portion from the second tooth portion in the other of circumferential directions.
 7. The gear mechanism of claim 6, further comprising a mating gear meshing the pair of gears, wherein: one of tooth surfaces of the first tooth portion projects outwardly from one of tooth surfaces of the second tooth portion; the other of the tooth surfaces of the first tooth portion substantially overlaps the other of the tooth surfaces of the second tooth portion; one of tooth surfaces of a tooth portion of the mating gear contacts only the first tooth portion; and the other of the tooth surfaces of the tooth portion of the mating gear contacts the second tooth portion.
 8. A blade drive device comprising: a board having an opening; a blade changing an opening area of the opening; and a gear mechanism transmitting a drive force from a drive source to the blade, wherein: the gear mechanism includes a pair of gears including first and second gears overlapped with each other in an axial direction; the first and second gears include first and second tooth portions, respectively; the first tooth portion slightly projects outwardly from the second tooth portion; and the first gear is formed with a deformation facilitating portion for facilitating deformation of the first gear in a radial direction.
 9. The blade drive device of claim 8, wherein the deformation facilitating portion is located between the first tooth portion and a rotation center of the first gear, and extends in a circumferential direction of the first gear.
 10. The blade drive device of claim 8, wherein the deformation facilitating portion is formed in the first gear, and has a hole shape.
 11. The blade drive device of claim 8, wherein the first gear has engagement means for fixing the first gear and the second gear by engagement, and the engagement means is arranged at a radially inner side from the deformation facilitating portion, and engages the blade to transmit a rotational drive force of the pair of gears to the blade.
 12. The blade drive device of claim 11, wherein the engagement means includes: a drive pin formed in the second gear; an engagement hole engaging the drive pin and formed in the first gear; and a cam slot engaging the drive pin and formed in the blade.
 13. The blade drive device of claim 12, wherein a projection amount of the first tooth portion from the second tooth portion in one of circumferential directions is different from that of the first tooth portion from the second tooth portion in the other of circumferential directions.
 14. The blade drive device of claim 13, wherein: the gear mechanism includes a mating gear meshing the pair of gears; one of tooth surfaces of the first tooth portion projects outwardly from one of tooth surfaces of the second tooth portion; the other of tooth surfaces of the first tooth portion substantially overlaps the other of tooth surfaces of the second tooth portion; one of tooth surfaces of a tooth portion of the mating gear contacts only the first tooth portion; and the other of the tooth surfaces of the tooth portion of the mating gear contacts the second tooth portion.
 15. The blade drive device of claim 14, wherein the other of the tooth surfaces of the second tooth portion is a tooth surface to which a drive force is transmitted by the mating gear or which transmits the drive force to the mating gear at a time when the area of the opening is reduced by the blade.
 16. The blade drive device of claim 8, wherein the gear mechanism includes: the pair of gears; and a mating gear meshing the pair of gears and connected to a rotary shaft of the drive source.
 17. The blade drive device of claim 8, wherein the first gear is formed to be thin, and is made of a material more elastically deformable than that of the second gear. 